1. Field of the Invention
The invention relates to bacterial degradation of hydrocarbons and, more specifically, to a pure culture of aerobic, mesophilic bacterium capable of biodegrading low-molecular-weight chlorinated, aliphatic hydrocarbons to CO.sub.2, HCl and H.sub.2 O.
2. Discussion of Background and Prior Art
The widespread use of chlorinated aliphatic hydrocarbons, and in particular trichloroethylene (TCE) and tetrachloroethylene (PCE), as solvents, degreasers and ingredients in the manufacture of plastics has resulted in substantial pollution of groundwter. These compounds tend to persist in groundwater.
Currently, to decontaminate groundwater contaminated with TCE and PCE, the groundwater is pumped to the earth's surface where the contaminants are stripped using aeration towers or removed on sorbent. Aerobic biodegradation, on the other hand, is an alternative to surface pumping that holds substantial economic and practical advantages.
Anaerobic bacteria for biodegradation of TCE and PCE are available. Unfortunately, the byproducts of anaerobic biodegradation are vinyl chloride and vinylidene chloride, compounds which are more toxic than their chemical parents. Nontoxic byproducts of the complete biodegradation, or mineralization, of chlorinated aliphatic hydrocarbons, CO.sub.2, HCl, and H.sub.2 O, are obtainable aerobically, but TCE and PCE are resistant to aerobic biodegradation.
Heretofore, conflicting results have been obtained in the search for an aerobic, chlorinated-aliphatic-hydrocarbon degrading bacteria. Some investigators have found no evidence of biodegradation of TCE or PCE. However Tabak, et al., reported the disappearance of over 50% of di-, tri- and tetrachloroethylenes from initial levels of 10 ppm in a period of one week using a mixed sewage innoculum and yeast extract as the primary substrate ("Biodegradability Studies with Organic Priority Pollutant Compounds", 1981, J. Water Pollution Control Federal 53:1503-1518). More recently, Wilson and Wilson found that 150 ppb of TCE was aerobically degraded to carbon dioxide in two days in an unsaturated glass column packed with sandy soil ("Biotransformation of Trichloroethylene in Soil", 1985, Applied and E nvironmental Microbiology, Vol. 49:242-243).
It is known that methanotrohs, methane using organisms, will oxidize and dechlorinate halogenated methanes using the enzyme, methane monooxygenase. It is also known that propane-oxydizing bacteria can epoxidate ethylene and that the epoxide is metabolized further.
Most metanotrophs are capable of utilizing only methane and other C-1 compounds as sole sources of carbon and energy. Methane monooxygenase is a non-specific enzyme which enables obligate methanotrophs to oxidize a wide variety of nongrowth compounds, including hydroxylation of n-alkanes, epoxidation of n-alkenes, and dechlorination of aliphatic and aromatic substances. Some of these oxidation products, such as n-alkenes, are incorporated into cell material and are considered supplementary substrates.
Since methanotrophs can oxidize ethenes and dechlorinate chloromethanes it seems likely that such bacteria would be able to oxidize chlorinated aliphatic hydrocarbons. However, until the present invention, the search for such bacteria has proved unsuccessful.